This invention relates generally to restorative dentistry and more particularly to implant prosthetic procedures.
The natural teeth of an individual are often lost as a result of dental disease or trauma, making it desirable to replace a natural tooth with a prosthetic device. One type of prosthetic device is a dental implant which is surgically positioned within the mandibular or maxillary alveolar bone of the patient and, after healing, is fitted with a tooth-simulating prosthesis or crown.
One type of dental implant, often called a submergible or two stage implant, has a separate root member which is implanted by an oral surgeon in the alveolar bone of the patient. Following healing, a head member or abutment is mounted on the root and then the crown is mounted on the abutment.
An implant of this type which has become widely used is shown and described in co-assigned U.S. Pat. No. 4,738,623. In this patent a root member having multiple, outwardly extending fins formed on the lower portion thereof has a narrowed upwardly and inwardly contoured shoulder formed above the fins and an abutment receiving female seat or socket formed through the top of the shoulder. Upon surgical insertion, autogenous graft material including conventional synthetic grafting material is packed in the void surrounding this narrowed shoulder. A small healing plug is positioned in the socket while the gingiva is permitted to heal over the entire implant.
When sufficient healing has occurred, i.e., in several months, the plug is surgically accessed and removed. A permanent abutment member having a male or post portion such as those formed with a locking taper, is then mounted on the root member with the post portion received in the socket, in the cited example, a socket formed with a locking taper. The abutment or head member has an upstanding generally tapered, conical exterior surface with an anti-rotational flat surface portion for mounting the prosthetic crown and a basal portion having a convex, frusto-spherical exterior surface which extends downwardly from the tapered portion. The center of the sphere which defines the frusto-spherical surface lies on the axis of the conical surface so that the frusto-spherical and conical surfaces intersect along a circle. When surgically implanted the spherical surface extends through the gingiva and alveolar crest toward the root member and provides an interface between the tissue and the abutment which has a circular cross section, regardless of alignment of the head member.
The healing plug is surgically accessed by excising the tissue over the plug, for example by using a small round bur or a scalpel and is removed by retracting the plug with forceps or using a conventional 700XL bur pressed into the center of the plug and turning the bur clockwise slightly. The site is then prepared as by using a sulcus reamer corresponding to the diameter of the basal portion to remove excess bone overlying the implant so that the head may be fully seated. After appropriate flushing and drying of the root socket the post portion of the head is inserted. If a flap procedure was used to access the submerged implant the flaps are trimmed to accommodate the protruding implant head and then stitched together with interrupted sutures and allowed to heal. The gum tissue is allowed to heal while the permanent crown is prepared using conventional techniques including the taking of an impression.
However, a problem frequently occurs regarding the interdental papilla. That is, the gum tissue tends to heal taut to the head of the abutment member so that when the permanent crown is placed on the abutment member the margin of the crown is not concealed. This negative aesthetic effect is exacerbated by the fact that conventional implants have a given width smaller than the teeth they replace. For example, in the anterior part of the mouth a central incisor is typically on the order of 8 mm across at the gum line and typical implants for such teeth are on the order of 4 mm at the location extending from the gum tissue. As a result an undesirable triangular apex configuration typically forms at the gum line detracting from the cosmetic appearance.